Bomb sight



ass Reference FIP8308 XR 2 162 6 ESTAVA8LABLE 00;:

June 20, 1939. w CHAFEE r AL 2,162,698

BOMB SIGHT 5 Sheets-Sheet 1 Original Filed June 18, 1932 INVENTORS fem MAGHHFEEQ HUGH MU/PTHGH Search Room June 20, 1939. E w, HAFE ET AL 2,162,698

BOMB SIGHT Original Filed June 18, 1932 5 Sheets-Sheet 2 5m MGM/ 55 //z/6//- Mamas/1 N J i r U TTORNEY 74 -5. 1' Wm Room June 20, 1 E. w. CHAFEE- Er AL 2,162,693

' BOMB SIGHT Original Filed June 18, 1932 5 Sheets-Sheet 3 INVENTORS 59m 14/. 671A FEE #0611 N04? meH l search R00 74 5 1 Cross Reference m 358T AVAILABLE CO1 June 20, 1939. w CHAFEE. r AL 2,162,698

BOMB SIGHT Original Filed June 18, 1932 5 Sheets-Sheet 4 lNVENTORS EHRL W. GHAFEE HUGH MURTHGH QEST AVAELABLE k,v

June 20, 1939. v 'E. w. CHAFEE ET AL 2,162,693

BOMB SIGHT Original Filed June 18, 1932 5 Sheets-Sheet 5 S INVENTORS EARL W. CHAFEH HUGH MURTHGH BY WMM MTTbRNEY Patented June 20, 1939 3EST AVAILABLE COF UNETED STATES PATENT @FFME BOMB SIGHT Earl W. Chafee, New York, and Hugh Murtagh, Brooklyn, N. Y., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application June 18, 1932, Serial No. 618,080 Renewed January 14, 1938 11 Claims. (Cl. 881) This invention relates to bomb sights for airof movement of the sight so that this value put craft which are designed to direct the course of into the computing unit (and used in lieu of the airplane so that its ground track (neglecting ground speed) is different at all altitudes alofifset) passes through the target in a straight though the ground speed may be the same. This 5 line before and at the instant of bomb release, is made possible in our machine because the caland preferably which also determine the exact culating mechanism in our bomb sight is based point at which the bomb should be released to entirely on rates and is independent of actual strike the target. Onaccount of the high efiiground distances and because as we solve the ciency of anti-aircraft gun fire bombing aircrafts range triangle altitude only enters as a variable are tc-day forced to high altitudes (on the order in obtaining the average rate of fall of the bomb 10 of 2%,690 ft.). At such altitudes the effect of which varies very slowly with altitude. By this wind is very important so that it is necessary means also, we are enabled to employ one varithat the aviator determine accurately both the able speed gear without the assistance of an ground speed and side drift of the plane and from altitude multiplying unit.

these factors determine the straight ground track Another improvement accomplished by our into the target, the correct range angle along that vention is a means for determining the drift track, and the correct deflection or offset angle angle directly from the bomb sight. Other obin case of side wind. In order that the plane jects and improvements will become apparent as may he brought as quickly as possible upon said the description proceeds.

20. straight ground track, we provide a connection Referring to the drawings illustrating several between the bomb sight and the steering mechforms the invention may assume, anism of the plane whereby the plane may be Fig. 1 is a perspective view of the exterior of turned in accordance with the movements of the our complete bomb sight. 7 bomb sight. Such turning maybe effected either Fig. 1A is a detail of the range angle and through a human agency, that is, through the sight angle indicator. 25 operation of electricalsignals and through the Fig. 2 is a diagrammatic perspective view of human pilot or automatically as desired, but for one of the units or parts of the calculating mechsimplicity we have shown only the former method anism referred to hereinafter as the offset unit. of control in this application. Fig. 3 is a diagrammatic perspective view of One of the principal objects of this invention the calculating mechanism from which, however, 5

is to simplify bomb sights of the above described the off-set unit and the trail unit are partially character so as to reduce the number of parts omitted.

and eliminate'mechanical errors as far as pos- Fig. 4 is a diagrammatic perspective view of sible. To this end the formulae used in the comthe aforesaid trail unit portion of the calculatputing apparatus have been greatly simplified, ing mechanism. substantially all variable pitch cams and me- Fig. 5 is a diagram showing the method of chanical differentials eliminated, and the variarriving at a straight ground track intersecting able Speed gears reduced to a mum. the target according to our invention.

Another important improvement over the prior Fig. 6 is a side elevation, partly in section, of

40 art consists in the method of synchronizin the principal portion of the optical unit together 40 ou Speed in instrument In the prior with the stabilizing or baseline gyroscope. 911 attempt was made to actually Set up Fig. 6A is an end view, partly in section, of the the true ground speed in the instrument. On Supporting frame for the gyroscope and reticule the other hand the actual rate of movement of unit the sighting prism for a given ground speed is Fig 7 is a sectional detail of the support for 445 much less at high altitudes than low altitudes. the mainprism or other reflector used for sight In fact, it is inversely proportional to the Ialtimg the target tude. Therefore, devices of the prior art ave been very inaccurate at high altitudes owing ggaa plan VleW of the ab hzed sighting to thenecessit of multi lying rism s eed by O a function of tlie altitude because this e120 mul- 8A 15 an enlarged detall of the central tiplied any errors by the same proportion. In portlon 0f the retlcule- I ouri sight, on the other hand, we do not attempt Fig. 9 is a bottom p n v w f the gyroscope to set up actual ground speed but deal entirely showing the looking or casing mechanism therewith the horizontal component of the actual rate for. 55

v n q --r aesmv CO Fig. 10 is a detail showing the quick release for the locking mechanism.

Fig. 11 is a diagrammatic view showing a modified form of the invention in Which the signals to the pilot are transmitted automatically from the bomb sight itself.

Figs. i2 and 13 are diagrams illustrating the general theory of operation of the sighting and calculating mechanisms, Fig, 12 being an elevation and Fig; 13 a plan view of the vectors involved.

Our bomb sight may be considered as made up of several units, all cooperating to produce the final result, namely, the optical system, the computing unit, and the pilot directing system, although both the optical system and computing unit are entirely contained in the casing I. The optical system comprises in general a telescope 2 mounted in the top of easing I, which, through an optical system (not shown), views an image of the ground appearing on a stabilized reticule 3. Said reticule is preferably the only part of the optical system connected to the stabilizing gyroscope or gyro vertical 4 (Figs. 6 and 8) and is shown as provided with cross hairs 5 and 5 placed fore and aft and transversely, respectively, of the aircraft. Said reticule may also be provided with graduated lines l for the purpose of presetting as will be described hereinafter. The ground image is thrown upon the reticule from a prism or other reflector 8 which is preferably pivoted about a transverse axis 9 so that the light of sight may be kept upon a fixed point on the ground as the aircraft approaches, and flies over the same. Saidprism is also preferably mounted for turning about a fore and aft axis on the craft so that the proper offset angle may be set up. As to this feature, the invention is similar to the prior patent to Mortimer F. Bates, No. 1,783,769, dated December 2, 1930 on Bomb sights.

As shown, the pivotal transverse shaft 9 on which the mirror is mounted, is journaled in a ring iii, which in turn is mounted for angular adjustment in an outer fixed frame ii. The adjustment of the prism about the transverse axis to follow the target is shown as effected through a rod I2 having a swivel connection I2 with the back frame 8' of the prism, the ball and socket being held together by spring 9. The adjustment about the longitudinal axis for the offset angle or deflection is shown as effected through an arm i3 secured to the back I4 of ring ii! (see Figs. 2 and 6). The line of sight from the ground enters through the window I4 and is reflected by the prism 8 to a second fixed prism i5 which directs the image along a vertical line through the objective lenses it which focus the image on the reticule 3.

Preferably we incorporate in the sight a means for quickly and accurately determining the correct drift angle. For this purpose we have shown auxiliary drift prism I? or other double reflector slidably mounted between the prism 55 and the lenses i6. Said drift prism is normally pushed out of this line of sight by means of the aieaces below the draft as seen through the window 23 is reflected up through the lenses I6 to the reticule. The bomber, in looking through the telescope, then sees objects on the ground passing across the optical field. As the motion of these objects in relation to the reticule is caused only by the forward motion of the plane over the earth, the roll and pitch of the plane being taken out by the stabilized reticule, the direction of motion across the field is parallel to the ground course the plane is flying. Therefore, if the sight as a whole is turned until the objects in the field of View move along or parallel to the fore and aft hair 5 on the reticule, then the sight will be pointed in the direction of the ground course or, in other words, the correct drift angle for that particular course will be set into the bomb sight. This is accomplished by rotating the handle A at the front of the instrument (Figs. 1 and 2) which turns shaft 25 and thereby rotates vertical shaft 26 through worm 21 and wormwheel 28. Shaft 26 is shown as having thereon a drift dial D and as carrying a pinion 29 meshing with a fixed gear 38 at the base of the device so that rotation of the handwheel A rotates the base I29 and the entire casing I in azimuth around said gear 30. After obtaining the correct drift angle, the prism I! is moved out of the way by moving handle I8 to the left in Fig. 6. In actual operation, the bomber may keep prism I1 at an intermediate position where it intercepts only a part of the field of view. In such case, by shifting his eye from the forward to the rearward line of sight through the telescope, he may see either the distant target or the ground beneath the plane at will or almost simultaneously. The apparent ground speed may then be set up through handle GS by which an automatic means is set into motion which causes the prism to remain on the target as the craft flies toward it, as hereinafter described.

Preferably the reticule is stabilized from a gyro vertical (Fig. 6) which is shown as a universally mounted gyroscope having the top thereof connected by linkage 35" to a gimbaled framework 36" so that the reticule 3 is stabilized in both planes which, in effect, stabilizes the optical system. The gyroscope 4 is shown as mounted for oscillation about a transverse axis I50 in an outer gimbal ring I5I which in turn is mounted for oscillation about a fore and aft axis on trunnions I52, I52 in fixed frame I53. Said gimbal is provided with forwardly extending arms I54 which support the frame 36" on transverse axis I55, so that a common gimbal is provided for both the gyroscope and reticule frame. Where the arms I54 pass under the cross bar 153 on frame I53, the bar is bent upwardly to furnish sufficient clearance for the bars to oscillate about main gimbal axis I 52, I52 (Fig. 6A).

The gyroscope is preferably locked until the sight is thrown into operation by means of looking or caging fingers 40 pivoted around the base thereof (Fig. 9). Said fingers are equally spaced around the gyroscope and bear at their inner ends against pin 4I projecting downwardly from the gyro casing. Said fingers are all operated simultaneously from a caging handle 42 (Figs. 6 and 10) operating through bevel gears 43 and a vertical shaft 44 which has secured adjacent its lower end a finger 45 which bears against a .pin 45 on one of locking fingers 40. The several arms are connected by cross links 41 and are normally held open by a tension spring 48 (Fig.

3EST AVAILABLE c 7 42 I u 1 I J 9). When handle 42 is'rotated, however, in the proper direction, the finger 45 pressing against pin 46 closes the locking fingers and thus cages the gyroscope, the handle being held in this positionby the engagement of a cross pin'52' in a notch H50 in fixed sleeve I60. In order not to disturb the gyroscope in the process, it is highly desirable that all fingers be released simultaneously and quickly and for this purpose We have provided a quick release button 50' slidably mounted at the center of the handle 42. This button, which is normally pressed outwardly by spring 5|, if pushed inwardly releases the cross pin 52' from notch I60, thus permitting the springs 48 and 49 to snap the fingers open.

The computing unit may be best understood by first describing the general mathematical principles involved as shown in Figs. 12 and 13. The vertical leg of the range triangle AOB represents the altitude (H) and the horizontal leg AB represents what may be termed true range distance, i. e., the horizontal projected distance of the aircraft from the target when the aircraft is at position 0. Point D represents the point at which the bomb would hit the ground if released at O and there were no air resistance. The whole range distance then, i. e. AD, equals the ground speed multiplied by the actual time of fall of the bomb or where GS=the ground speed. T =time of fall. Rw =the whole range.

The true range then (R) is equal to the whole range minus the trail distance (GS X T) Y=R where Yzthe trail distance. From Fig. 12 then R tan 0- where 0=the range angle, and substituting the values given above (GSX T)-Y R.,,Y

This expression may be written as follows by dividing both the numerator and denominator by T so that the expression becomes tan 0:

Y GS Y I tan 6: Gs a: r 7f ATT E l T T This equation may also be written V -R IA. tan 0=M 0r 1 VP where VH represents the horizontal component of the rate of movement of the line of sight inthe horizontal component of the rate of movement of the sight is taken as the ground speed, while for all other altitudes the apparent ground speed would be inversely proportional to the altitude, which we take into account not by altering the indicated rate (VH), but by multiplying both numerator and denominator by thus introducing altitude only in the expression Vv or average rate of fall of the bomb and in computing the proportional RH. Experimentally, it has been determined that Vv varies very slowly with altitude changes so that errors in obtaining altitude affect the accuracy of the sight very little. Viewed from another standpoint, the average range triangle is small so that the vertical side is much longer than the base. Therefore, a given error on the vertical side will cause much less error in computing the range angle than the same error on the short side of the triangle.

Referring now to Fig. 13, it will be seen that for cross wind bombing the trail is always calculated along a line parallel to the air speed line and of a length proportional to air speed. In other words, the bomb will fall down wind from the ground speed course a distance called the offset) equal to the trail times the sine of d where d equals the drift angle.

Letting a equal the offset angle, that is to say, the angle between the vertical plane containing the ground course AD and an inclined plane containing the ofiset line AB on the ground and intersecting said vertical plane along a line containing the point 0, which is the point of release, it may be stated that tan a=g sin d or since, approximately,

where c is a constant, and As is the air speed of the airplane, we may write tan A, sin d or for unit altitude, II. tan a= i+ It is found that over the ranges of values of air-speed, terminal velocity, and altitude that are liable to occur in practice, it is a good approximation to assume that for any given bomb where C is a constant for the particular type of bomb. This constant 0 depends on the terminal velocity TV of the bomb, and is approximately proportional to it so that we can write C is equal to C-TV.

seer AVAILABLE GDP From the above equations we derive, as a sufficiently close approximation, the relation A -sin d TV-C The computing mechanism is so designed that the range angle (0) is set up automatically by setting in the correct combination of altitude (H), air speed (As), component prism speed (GS), and type of bomb (T1,).

The range arm (Fig. 3) consists of a slotted lever having a hub or sleeve 5! loosely mounted on shaft 52. On said hub is also mounted one 53 of a pair of contact arms 53 and 54, each having an upper bent portion 53 and 54', respectively, which may be seen through a window 55' in the top of the box I. The free end of said lever 58 is positioned by a block 55 slidably mounted in the slot 56 in said lever. Said block has a pin 57 projecting on each side thereof, said pin engaging in front a slot 58 in a vertically movable horizontal bar 59. At the opposite end said pin engages a vertical slot in a horizontally movable vertical bar SI. Bar 59 may be moved vertically in accordance with the vertical velocity of the bomb from a threaded shaft (or shafts) 82 which is rotated through bevel gears 63 from shaft I54 of altitude handle wheel H in accordance with the altitude as set on dial 66 which is turned therefrom through pinion 55. Slotted bar 6!, on the other hand, is moved laterally by the rotation of a threaded shaft 5! which is positioned by the handle GS in accordance with the apparent ground speed.

For this purpose we provide a variable speed drive actuated from a constant speed motor 3! which drives through suitable gearing 32 a disc 33 (Fig. 3). Bearing on said disc is a change speed ball (or balls) 34 which is placed between said disc and a cylinder 35 and is adjustable axially along the cylinder and radially of the disc by means of a threaded shaft 36. The rate of rotation of shaft 35' is, therefore, proportional to the apparent ground speed and a speed indicator S may, therefore, be placed on this shaft to show ground speed for a predetermined altitude by which the device may be checked. The trial setting of the change speed device is effected through the handwheel GS on the instrument, which is shown as mounted on shaft 3? which is geared to threaded shaft 38 through gearing 36. Turning of handwheel GS also automatically sets up in the computing mechanism the correct angular rate of prism speed by positioning bar 6! laterally through threaded shaft 57. Also, the variable speed device actually turns the prism 8 at a rate to keep it on the target through gear 70 on the shaft 35 of cylinder 35, large gear II, gear '12 and other mechanism hereinafter described, the target having been initially sighted by turning target pick-up handle P on gear H.

On a screw '58 is threaded a block '56 carrying a pin Z5 which engages a hoie in block it slidably mounted in a slot T! in arm 18 so that said arm is turned at the same angular rate as the line of sight when the correct apparent ground speed has been set up and the sight is on the target. This arm is secured to the shaft 52 which turns through suitable gearing a gear sector BI pivoted at 82 and linked to the prism 8 through the above described rod 12, thus setting and keeping the line of sight on the target after having been set thereon by prism pick-up handle P and the proper apparent ground speed having been set in. While prior sights usually interpose a differential between the prism pickup handle P and the change speed gearing 33-35, we prefer not to do so, the handle P, when operated, merely slipping the variable speed gear. By this we eliminate a large source of error in prior sightsdue to unavoidable lost motion or backlash in all differentials.

Arm 18 above described also positions contact arm 54 above described, both arms being on the common shaft 52. Arm 54 is, therefore, advanced toward arm 53 (positioned at the range angle (9) as the target is approached until contacts I20 and I22 thereon successively engage their complemental contacts I20 and I22 on arm 53 to give a warning signal I2! and drop the bomb (or signal to do so) through solenoids I2I and I23. To insure this sequence, contact I20 may have a spring pressed pin X projecting therefrom. Preferably signal I 2I is in the form of a miniature fiag (Fig. 6) which is projected into the line of sight of telescope 2 by solenoid I2i'. Since arm I8 is always maintained at the sight angle and arm 54 is on the shaft 52 thereof, the position of end 54 in curved window 55 may be used as an indicator of the sight angle or angular speed. For a given angular speed, however, the corresponding ground speed varies not only with altitude but with a function of the instantaneous sight angle. By having a nonuniform scale IBU on window 55 on which index 54 is readable and by bearing in mind his altitude (H), the bomber may obtain a ready estimate of the horizontal component of his velocity (GS) and ground distances.

The trail unit portion of the device is shown diagrammatically in Fig. 4. In this unit are introduced a terminal velocity of fall of the bomb through the handle TV which is set in accordance with the known characteristics of the bomb in accordance with the readings on dial T, while indicated air speed is set into the unit from the handle AS. Turning of the handle TV rotates through suitable gearing 85 and 86 a sector 8'! with respect to the altitude dial 65. Said sector has a window I65 therein having a central vertical cross hair I65 and graduations G spaced vertically in accordance with a function of known terminal velocities for different types of bombs. The dial '66 is also graduated with curved and non-uniformly spaced altitude curved lines I58 and after the sector 8'! is set from handle TV so that the dial T indicates the required terminal velocity (in hundreds of feet per second), the handle H is turned until the known altitude is indicated by reading the proper altitude curve against the proper terminal velocity mark G on the vertical cross hair I 66. By this means the factor T (time of fall) of Equation I is introduced into the calculating mechanism along with H. Thus bar 59 is positioned in accordance with Vv of Equation I. This is one respect in which our improved sight differs from. the prior art in which a second variable speed device (in addition to the one for apparent ground speed) was used to compensate for the fact that the rate of movement of the line of sight varies with the altitude. Such a device, when used at great altitudes, multiplies the errors. In our device only one variable speed device is used, the variations due to altitude being taken care of by the proper spacing of the altitude markings I58 on dial 65.

Said handwheel TV also rotates through suitable gearing 89 and 90 a threaded shaft 9| on which is threaded a block 92 carrying a pin 93 so that as said shaft 9| is rotated the pin is ad- '3ES'I' AVAILABLE CO? justed along a slot 94 in a lever 95 and acts as a variable fulcrum therefor. The far end of said lever is shown as bearing against a pin 90 on a second block 91 threaded on a shaft 98 which is turned from the air speed setting handle AS. The opposite end of said lever is shown as pivotally secured to a rack bar I00, the teeth of which mesh with a pinion IIII on the shaft of the trail drum I02. On said drum are plotted indicated air speed curves I03 in miles per hour (for instance) which curves are readable on an altitude scale I04 running lengthwise of the drum. Therefore, after the proper value of TV has been set in on drum T, if the proper indicated air speed is set on the drum I02 by turning handle AS against the known altitude H on the scale, the rotation of handle wheel AS will put the rate of horizontal retardation (RH) of the bomb into the screw '51 by the gearing 99, shaft III and rack and pinion gearing I I2 connecting handle AS and screw 61. Thus bar 6| is positioned in accord ance with Vl-I-R,I-I of Equation I.

The offset unit is primarily actuated from the rotation of the sight as a whole in azimuth. When this occurs the shaft 2'8 above described is rotated, thus rotating through the gear I05 a large gear I06. Mounted eccentrically on the shaft I01 of said gear is a U-shaped member I08 forming part of the calculating mechanism and which is, therefore, rotated through an angle equal to the drift angle. In said member I08 is journaled a threaded shaft I09 which is set from a handle or knob 0. On said shaft is threaded a block IIO carrying a pin III which engages a slot 2' in a T-shaped slide H3. Said slide is slidably mounted in framework II4. Rotation of the member I08 about the center of shaft I01, therefore, will move the slide I I3 longitudinally in accordance with the distance of the pin III from the center of shaft I01 and also in accordance with the sine of the drift angle. Mounted on block H0 is a scale H5 in speed units, such as miles per hour, while mounted on member I08 is a scale I I6 graduated to represent the ballistic coeificient of the bomb, i. e., terminal velocity TV. Therefore, by setting the handle 0 to the proper readings on scales I15 and H6, i. e. actual air speed and terminal bomb velocity, there is introduced the element of Equation II, while the factor sin (1 is introduced automatically by positioning the sight in azimuth, which rotates the member I08 about the center I01. Therefore, the movement of slide H3 is proportional to a function of the offset angle a, and this movement is transmitted to the lever I3 at the pin and slot connection I3, said lever I3 being secured to the mirror 8 to tilt the same laterally for setting up the proper offset angle or deflection.

The operation of the computing portion of our device is as follows: The bomber usually sets in first the terminal velocity of the bomb through rotating the handwheel Tv until the dial T indicates the proper terminal velocity for the type of bomb employed as shown by tables furnished the bomber. This also positions the fulcrum 93 of the multiplying lever 95 and moves the pointer or arm 8'1 on the altitude dial 8'8. At the same time the handwheel O is actuated to set the proper value of actual air speed with reference to Tv on scale I I6. Next, the altitude is preferably set in by turning handwheel H until the dial 6S indicates the correct altitude as the altitude marks I68 are read against the vertical graduations G for TV. This operation turns the threaded shaft 62, thus positioning the pin 51 vertically for the values of V, or Turning the air speed handwheel As revolves the horizontal screw t? as described, thus positioning the pin 5: horizontally in accordance with At the same time the far end of the trail lever 95 is moved, causing the trail drum I02 to rotate, the curves of which are corrected for variations between true and indicated air speed and for Tv. By matching the proper air speed curve on the drum with the correct altitude on the flat scale I04, the vertical shaft III rotates the horizontal screw 57 through rack and pinion gear III a distance equal to the average rate of horizontal retardation of the bomb The apparent ground speed is obtained by moving the variable speed ball 34 by turning handle GS until the angular velocity of the line of sight matches the speed of the plane. This sets the ball at a distance from the center of the disc 33 proportional to the velocity of rotation of the prism. As the horizontal screw 01 of the range arm mechanism is directly connected to the ground speed screw 36 of the variable speed drive through gearing 36, the slider on the range arm 50 will also be set horizontally for GS Y (or AGS) minus the horizontal retardation rate, or

It should be noted that although we have retained the three primary settings of altitude, air speed, and a function of ground speed, we have laid the greatest mechanical responsibility on that particular setting which can be determined the most accurately. In bomb sights, the altitude setting consists of the reading given by an altimeter which has varying errors and, therefore, the altitude so obtained is not very accurate. The same applies to the air speed settings and if ground speed, proper, is used (as in most bomb sights) it also is often erroneous as it has to be multiplied by the altitude factor. In our system, on the other hand, we use only the horizontal component of the angular travel of a prism, which is held on a definite object on the ground in which there can be no error other than due to this setting and reading, and being an optical device is very accurate. We make, therefore, this setting the basic factor of the settings so that the errors caused by the other settings can only be of fractional proportions. As far as the range the same at an equal QEST AVAILABLE COP angle is concerned, if the bomb were dropped in vacuum this horizontal rate would be the entire travel of the bomb and the altitude would enter only once in the velocity of fall of the bomb.

The above settings, therefore, will position the range arm at the correct range angle or 0, thereby positioning the contact arm 53 at the same angle. The cooperating contact arm 54 is positioned by the position of the prism arm '18, which in turn is positioned from the variable speed drive through block 14 and the screw I3 as described. As the angle of the line of sight approaches the range angle, first the warning contacts I20I2Il are engaged, showing a flag I2I in the telescope 2 by exciting solenoid I2I' and lighting the external lamp I44. As the proper range angle is reached, the second pair of contacts I22I22 are engaged either sending a signal to the bomber or operating the solenoid I23 to release the bomb or both.

Since, however, there is always a slight delay between the actual crossing of the range angle and the release of the bomb, we prefer to provide a means for presetting the bomb to allow for this delay. Such a means preferably consists of the above described presetting scale I engraved on the reticule 3. Each scale division has a value of a predetermined unit of distance, such as 10 ft. at 1000 ft. altitude at an average range angle. Therefore, in order to obtain the value of the divisions at any other altitude, it is necessary mentally to multiply 10 by the first one or two figures of the particular altitude (H). For instance, the value of each division at 5000 ft. would be 50 ft. and at 15,000 ft. would be 150 ft. To preset the line of sight any given amount, it is necessary to set the target on a predetermined line on scale I instead of on the cross hair 6.

By special design of the reticule, we also are enabled to use the sight as a means of furnishing the aviator with an estimate of the size of the objects and the distance between objects on the ground. To this end the cross hairs 5 and 6 stop short of the pointof intersection between distance from such point (see Fig. 8A). Preferably the distance between the adjacent ends of each cross hair is equal to the space between the major graduations on scale I. Therefore, if each major division repre sents 100 ft. at 10,000 it. altitude, a building whose image occupied a space between said two adjacent ends, would indicate to the aviator that its length was 100 it. if at that altitude.

Referring now to the pilot directing portion of our invention, the bomber signals the pilot as to the course desired by means of a manually operated switch I25 (Fig. 1), which has a plurality of contacts I28I2'l on either side thereof to indicate or control the degree of turn desired. If desired, the turning signals may be given automatically from the bomb sight. This form of the invention is illustrated diagrammatically in Fig. 11. According to this form, the fixed base ring is shown at 39, the same being provided with a worm I28 turned from the handle A to rotate the platform I29 which carries the bombsight, said worm meshing with worm teeth I3I on the ring I29 on platform I29. In this case, however, we provide within the ring I29 an auxiliary platform I32 which is rotatably adjustable on or within ring I29. Said ring I29 is shown as provided with internal teeth I33 with which meshes a gear I34 journaled on the platform I32. Meshing with gear I34 is a pinion I35 which may be rotated from the azimuth pick-up handle AP. Also on platform I32 are concentric segmental contacts I36 and I31 with which contact fingers I38 and I39, mounted on ring I29, are adapted to contact. Each finger is in circuit with one of the signal lamps E40 or I4I mounted adjacent the pilot, preferably adjacent the directional gyroscope I43 by which the pilot steers (Fig. 5). Normally the handle AP is in a position so that all the lamps are lighted (if switch I59 is closed) with handle AP vertical (in Fig, 11) and the contacts symmetrically positioned, but if said handle be turned in one direction (for instance to the position shown in Fig. 11), first one and then the other of the lamps I4I are extinguished, or if turned in the other direction, first one and then the other of lamps I40 are put out. It will also be apparent that turning of the handle A for setting up the proper drift angle does not affect the lights and also that the turning of the handle AP will not permanently disturb the correct drift setting because in operation the handle AP is always brought back to its initial or vertical position before the bomb is dropped.

The operation of our invention may be understood by describing a typical target approach. In Fig. 5, line I42 shows diagrammatically the ground course of the airplane approaching the target and the circles beneath the line illustrate the signals sent to the pilot beside the directional gyroscope I43. The parts above the line represent the appearance of the field as seen through the telescope when setting the drift and when sighting on the target. At the point A, the pilot sights the target and starts to fly toward it. During the time of flight between A and B, he sets up his drift as well as possible, trying to put the ground course of the plane straight through the target. Assuming he has the ground course approximately through the target at the point B, that is, within plus or minus 5 degrees, he then flies straight by means of his directional gyroscope I43 and closes a switch (not shown) to light the bombers signal lamp I44. The bomber, upon getting the signal, moves the prism I'I into the line of sight and then turns the azimuth control handle A until any sighted object M on the ground passes across the field of the telescope parallel with the fore and aft line 5 of the reticule. This operation is taking place between the points B and C, and at point C the 1:,

correct drift has been obtained. The bomber then closes the switch I50 (Fig. 11) to light the signal lamps I40, I4I at the directional gyro. At this time also the bomber moves the prism I? out of the line of sight and turns the prism handwheel P until he sees the target. The target will be somewhere in the field but off the reticule wires as indicated by the point T in Fig. 5. The bomber then signals the pilot to turn either by moving the switch I25 in Fig. i to the right or left or in the form shown in Fig. 11 by turning the handle AP which brings the line of sight on to the target as shown at T1, position C and also puts out the lights I4I (point C), thus signalling the pilot to turn rapidly. The pilot then puts the ship into a fast turn and continues turning at that rate until the outer lamp lights when he slows down the rate of turn (0). The bomber, in keeping the reticule on the target, keeps turning the pick-up handle AP in the opposite direction from the original movement (C until finally the ship has been brought around to the proper course (D), the target is at the exact center of the cross hairs and all lights are lighted, the original drift setting re- Cir BEST AVAILABLE COF maining undisturbed. During the time from C to D, while the bomber was holding the reticule on the target he is also synchronizing the ground speed by adusting handle GS. Therefore, he arrives at the point D at the correct ground speed set in the bomb sight and flying on the desired straight ground track directly toward the target (neglecting the offset or deflection). From this point D, to point E, where the bomb is released, the pilot maintains the ground course through the target both by watching his directional gy roscope and the signal lights which are operated automatically from the bomb sight in the form of the invention shown in Fig. 11 or from handle in the form shown in Fig. 1, the bomber in effect directing the plane to maintain its straight ground track until the bomb is released.

In accordance with the provisions of the patent statutes, we have herein described the principle and operation of our invention, together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other means. Also, while it is designed to use the various features and. elements in the combination and relations described, some of these may be altered and others omitted without interfering with the more general results outlined, and the invention extends to such use.

Having described our invention, what we claim and desire to secure by Letters Patent is:

1. In a bomb sight for aircraft, a pivotally mounted reflector to sight and follow a remote target as it is approached, an independently mounted reticule on which the ground image from said reflector is focused, a gyroscope connected to said reticule to stabilize the same against rolling and pitching of the craft, and a slidably mounted auxiliary reflector adapted to direct an image of the ground vertically below the craft onto said reticule in one position and to lie entirely out of the field of vision of said sight in its other position.

2. In a bomb sight for aircraft, a pivotally mounted reflector to sight and follow a remote target as it is approached, an independently mounted reticule on which the ground image from said reflector is focused, a gyroscope con nected to said reticule to stabilize the same against rolling and pitching of the craft, an auxiliary reflector adapted when in operative position to direct an image of the ground vertically below the craft onto said reticule and movably mounted between said reticule and the ground, and means for moving said auxiliary reflector into and out of the line of sight between the first named reflector and the reticule.

3. In a bomb sight for aircraft, a pivotally mounted reflector to sight and follow a remote target as it is approached, a reticule on which the ground image from said reflector is focused, means for stabilizing said reticule against rolling and pitching of the craft, a movable auxiliary refiector adapted in one position to direct an image of the ground vertically below the craft onto said reticule and in another position to lie without the field of vision, means for rotating the sight as a whole about its vertical axis to align the sight and the ground course, and means actuated thereby for adjusting said pivoted reflector to set the drift angle into the sight.

4. In a bomb sight for aircraft, a sight-directing member, means for mounting said member for turning about a vertical axis, means for mounting said member for adjustment about both the fore and aft axis of the sight, and an axis at right angles thereto, and means actuated by the turning of said member about its vertical axis for adjusting saidmember about said fore and aft axis to give said member the proper offset angle to compensate for the drift, including a pin rotated about a center in accordance with adjustment of said member about its vertical axis, means for varying the position of said pin in accordance with a function of air speed and bomb characteristics including a fixed scale and a cooperating scale mounted to move with said pin, one of which is graduated in air speed and the other in bomb characteristics, and a member positioned by one component of the movement of said pin for tilting said sight directing member about its fore and aft axis.

5. In a bomb sight, a stabilized reticule, cross hairs thereon interrupted at predetermined points adjacent the virtual point of intersection of said hairs, and a graduated scale adjacent one of said hairs, the spacing of said graduations having a predetermined relationship to the space between the adjacent ends of said cross hairs and to the size of an object on the ground at a predetermined altitude whereby the size of objrcts on the ground may be estimated.

6. In a bomb sight, a rotatable indicating meme ber, means for moving the same at the same angular speed as the line of sight moves in following the target, a second rotatable member positioned at the range angle and a scale on which both members are readable in which the graduations are nonuniformly spaced to compensate for the variations between actual and apparent ground speed with changes in the sight angle.

'7. A bomb sight for aircraft including a sight directing member, dual means for mounting the sight for turning about a vertical axis, comprising means for turning said sight parallel to the ground course to obtain the drift angle, and additional means for temporarily turning said sight to bring the target on the sight cross hairs, means operated only by said second named means for turning said member through the offset or deflection angle to compensate for side drift, and means operated only by said third means for indicating that a turn should be made.

8. In a bomb sight, a sight-directing member mounted for turning about a normally vertical axis and about the fore and aft axis of the sight and transversely thereof, means for turning said member about said vertical and transverse axes, means for varying the offset angle of said member about said fore and aft axis as said member is adjusted about its vertical axis in accordance with a function of the sight angle about said. transverse axis, independent means for adjusting said sight member about its vertical axis without so affecting said offset angle, and means operated by said last named means for indicating that a turn should be made.

9. A bomb sight for aircraft, including a reflector, dual means for mounting the sight for turning about a vertical axis, means for rotating said reflector about another axis to compensate for side drift, means operated by one of said dual means for actuating said second mentioned means to rotate said reflector through the oifset angle to compensate for side drift, and means operated by the other of said dual means, indicating that the craft should be turned without disturbing the setting of said reflector.

EST AVAlLABLE CO? 10. In a bomb sight, an altitude dial, means for setting said dial, said dial being provided with non-uniformly spaced altitude graduations thereon corresponding to the average rate of fall of difierent types of bombs from the indicated altitudes, a movable index device on which said dial is readable. means for setting said index device in accordance with the terminal velocity of the type of bomb used, a range angle bar, horizontal and vertical component means for positioning said bar, said horizontal component means serving to position said range bar in accordance with the ground speed of the aircraft,

ti CmjZaid range bar in accordance with the rate of fall of the bomb, and means interconnecting said dial setting means and said vertical component means for positioning the latter means simultaneously with the setting of said dial.

11. A bomb sight as claimed in claim 10, wherein said movable index device has radially spaced terminal velocity graduations upon which the graduations on the dial are read.

sair "ewertical component means serving to posi- EARL W. CHAFEE. HUGH MURTAGH. 

